1. Field of the Invention
The present invention is in the field of semi-conductor devices generally and is specifically directed to thyristors.
2. Description of the Prior Art
With reference to FIG. 1, there is shown a typical prior art thyristor.
The prior art thyristor is comprised of a p type anode emitter layer 12, and n type anode base layer 14 adjacent to the emitter layer 12. A p-n junction 16 is between regions 12 and 14. There is a p type cathode base region 18 adjacent to region 12 and a p-n junction 20 between regions 14 and 18. There is an n type cathode emitter region 22 formed on a portion of one surface of region 18 and a p-n junction 24 between regions 18 and 22.
A metal anode electrode 26 is affixed in an electrical ohmic contact relationship on surface 28 of region 12.
A metal cathode electrode 29 is affixed in an electrical ohmic contact relationship with surface 30 of region 22.
A metal gate contact electrode 32 is affixed in an electrical ohmic contact relationship with surface 34 of region 32.
A "turn-on" time prescribing a control speed of such a thyristor depends greatly upon a time interval "t.sub.1 " for which electrons from the cathode emitter region 22 injected into the cathode base region 18 are diffused through the cathode base region 18 to reach anode base region 14, and a second time interval "t.sub.2 " for which holes from the anode emitter region 12, injected into the anode base region 14, are diffused through this region 14 to reach the cathode base region 18. On the other hand, in order to increase a withstanding voltage upon the application of a forward voltage, it is necessary to thicken, as a matter of course, the thickness of the anode base layer 14 and to thicken the thickness "W.sub.B1 " of the cathode base region 18 between the cathode emitter region 22 and the anode base region 14 while rendering the impurity concentration of the cathode base region 18 sufficiently large which brings increases in the above-mentioned time intervals "t.sub.1 " and "t.sub.2 ".
Thus, in conventional thyristor, the speeding-up of the control speed is contradictory to a high withstanding voltage. Also there has been a problem that a speed at which the principal current is interrupted cannot be high because the quantity of holes injected into the anode base region 14 from the anode emitter region 12 is large.
With the above-mentioned problems in view, the present invention has been made to provide a thyristor capable of speeding up its control speed without lowering the withstanding voltage lower by making a structure such that, upon the application of a forward voltage, a voltage applied to a base layer on which a gate electrode is provided can be rendered small.